With Path MTU Discovery, the router can monitor the value set in the MSS option in TCP SYN and SYN-ACK messages, which enables it to reduce the MSS value below the TCP-MSS thresholds.
| Setting | Description |
|---|---|
| Enable Path MTU Discovery | Select Enable Path MTU Discovery to enable the Extreme Networks router to learn the maximum packet size, or maximum transmission unit (MTU), that can be sent between two hosts without fragmentation. |
| Monitor the MSS Option in TCP SYN and SYN-ACK Messages and Perform Clamping if the MSS Threshold is Exceeded | Select Monitor the MSS Option in TCP SYN and SYN-ACK Messages and Perform Clamping if the MSS Threshold is Exceeded to monitor the MSS option in TCP SYN and SYN-ACK messages and, if necessary, reduce the MSS value as determined by one of the following TCP-MSS thresholds. |
| MSS Threshold for All TCP Connections | Type the TCP-MSS threshold for all TCP connections passing through the device. If you do not specify a threshold value, TCP-MSS clamping uses Path MTU (40 bytes) for the IP and TCP headers. |
| MSS Threshold for TCP Connections Through the VPN Tunnel | Type the TCP-MSS threshold for TCP connections that pass through a Layer 3 VPN tunnel. If you do not specify a threshold value, the device uses the value set for the MSS threshold for all TCP connections. |